1. Field of the Invention
The present invention relates to hydrodynamic bearing devices, spindle motors, and recording and reproducing apparatuses, and in particular, to hydrodynamic bearing devices utilizing dynamic pressure of a fluid and used in spindle motors and the like for driving the rotation of disk shaped recording media, and the spindle motors and recording and reproducing apparatuses using those hydrodynamic bearing devices.
2. Description of the Related Art
In recent years, as the memory capacity of recording and reproducing apparatuses such as disk drive devices driving the rotation of magnetic disks, optical disks, magneto-optical disks, and other disk shaped recording media increases, the data transfer speeds thereof are also becoming faster. For this reason, hydrodynamic bearing devices, which are capable of supporting shafts driven to rotate at high speed with a high degree of accuracy, are being used as the bearing devices of motors used in this type of disk drive device.
In a general hydrodynamic bearing device, oil is filled as a lubricating fluid constituting a lubricant between an outer peripheral surface of a shaft and an inner peripheral surface of a sleeve that constitutes a support section for supporting the shaft, and dynamic pressure is generated by herringbone-shaped grooves formed on either the outer peripheral surface of the shaft or the inner peripheral surface of the support section, forming a radial bearing supporting a load of a rotating body in a radial direction upon rotation. Furthermore, oil is filled between a disk-shaped thrust plate secured to an end of the shaft and the support-section sleeve, and dynamic pressure is generated by spiral-shaped grooves formed on one of the opposing surfaces of the thrust plate and the support section, forming a thrust bearing supporting a load of the rotating body in an axial direction (rotation axis direction) upon rotation.
Hydrodynamic bearing devices can have either a fixed-shaft type or a rotating-shaft type, and in, for example, a hydrodynamic bearing of the rotating-shaft type and having a bag structure (one end of the bearing is closed), it has been disclosed that the relationships of clearances for preventing leakage of oil between clearances labeled A to H of the bearing interior, as shown in FIG. 11, are G<H; A<B and A<D; C<B and C<D; B<H and D<H; E<D, E<F, and E<H; and G<F, G<D, and F<H. When the above relationships are satisfied, sealing pressure is, as shown in FIG. 12, large at E, G, A, and C sections, and since oil collects at these sections with small gaps, the leakage of oil is prevented.    Patent document 1: JP 2004-183865A